The present invention relates to reluctance type electromagnetic actuators, and more particularly to sensing the position of an armature in such actuators.
Many types of machines have moveable members which are operated by a hydraulic cylinder and piston arrangement. Hydraulic fluid is supplied under pressure via a valve to the cylinder and pushes against the piston to move the machine member. By varying the degree to which the valve is opened, the flow rate of the hydraulic fluid can be varied thereby moving the piston at proportional speeds. Typically the valve is operated manually by a lever that was mechanically connected to a spool within the valve.
A current trend is away from using manually operated hydraulic valves toward electrically controlled solenoid valves. Solenoid valves are well known reluctance electromagnetic actuators for controlling the flow of a fluid. A solenoid valve involves an electromagnetic coil which moves an armature in one direction to open a valve. The valve may be opened to various degrees by varying the magnitude of the electric current flowing through the coil of the solenoid. Either the armature or a valve member is spring loaded so that when the current is removed from the solenoid coil, the valve closes.
In an electrohydraulic controller, there is no mechanical connection between the operator control mechanism and the valve. Therefore when an operator moves the control mechanism to a given position, there is no way of knowing, by tactile, visual or other feedback, whether the valve opened the corresponding amount. The actual position of the valve may vary in response to different operational characteristics. The obvious solution would be to attach mechanical position sensing devices to the valve to provide a feedback signal indicating the relative position of the valve. The electrical valve control circuit then could compared the sensed valve position with the desired position commanded by the operator and adjust the electric current applied to the solenoid coil until the desired position is achieved. Although such mechanical position transducers could solve the basic feedback problem, it is desirable to provide an entirely electrical, i.e. non-mechanical, technique for sensing the position of an armature in such actuators. That alternative approach would not be prone to mechanical failure and would be easier to maintain, and would be more cost effective.